Purification of coal tab bases



Patented May 26, 1942 PURIFICATION OF COAL TAR BASES Joseph H. Wells andPhilip J. Wilson, Jr., Pittsburgh, Pa., assignors to Carnegie-IllinoisSteel Corporation, a corporation of New Jersey No Drawing. ApplicationJuly 22, 1941, Serial No. 403,586

2 Claims.

This invention is concerned with the problem of recovering pyridinebases from coal tar distillation oil fractions containing these basesalong with at least 2% phenol and small volumes of other constituentsthat are soluble in the phenol. It is, of course, necessary to recoverthe pyridine bases so that they are relatively free from the phenol andthe other constituents men tioned, these other constituents beingimpurities, neutral oils and gummy compounds.

According to the invention, this problem is solved by washing such afraction with dilute sulphuric acid at an elevated temperature of from60 to 100 C., until a solution is obtained containing in equilibriumconcentration pyridine sulphate and the phenol with the describedconstituents dissolved therein. In addition to the pyridine, thissolution will contain in sulphate form any other coal tar base that waspresent in the fraction when it was washed.

The elevated temperature of the above washing is the cause of thesulphate solution obtained containing the phenol with the phenol-solubleconstituents dissolved therein. However, the elevated temperature of thewashing has been found necessary in the case of the fractions containing 2% or more of phenol, since in such instances the phenolcombines with the pyridine bases to form complexes which cannot beeasily decomposed by the prior art lower temperature acid washingsuccessfully used in the case of fractions containing lower percentagesof phenol.

The sulphate solution obtained by the prior art practice of acid washingat room temperature the fractions containing relatively little phenol,is 1 customarily purified by steam rectification. This produces anadequately pure pyridine su phate solution for pyridine recoverypurposes, it serving to largely remove the relatively small amounts ofcontamination resulting from such acid washing. However, the sulphatesolution obtained by the practice of the present invention cannot betreated in this manner, because it contains such large volumes of phenoland the described constituents that so much steam and time would berequired as to make the practice economically impractical.

With the above in mind, the sulphate solution resulting from theelevated temperature acid washing, is cooled to a temperature no higherthan 40 C. and is then washed with a relatively small volume of theoriginal oil fraction, or any similar fractions; for instance, it beingpossible to use the acid-washed fraction low in pyridine for thispurpose, providing it is cooled to a temperature not greater than 40 C.The result of this washing is to unbalance the equilibrium between theconcentration of the phenol carrying the dissolved constituents and thepyridine sulphate solution, whereby this contamination passes back intothe washing oil fraction. Therefore, separation of the pyridine sulphatesolution from the washing oil results in a solution that is sufficientlyfree from contamination to permit, it to be rectified with steam withoutan excessive consumption of either steam or time. The washing oilfraction will contain, in addition to the phenol and the phenol-solubleconstituents, some pyridine bases which may, however, be recovered byreturning the washing oil fraction to the system so that it can besubjected to the elevated temperature acid washing.

As a specific example of the invention, 500 gallons of a coal tardistillation oil fraction, containing 4% by volume of pyridine and 21%by volume of phenol, along with the usual amounts of phenol-solubleconstituents, is washed with three successive portions of 90 gallonseach of a 25% sulphuric acid solution at 80 C. The pyridine in the oilfraction is thereby reduced to by volume.

This results in 110 gallons of a black, cloudy pyridine sulphatesolution containing 33% by volume of pyridine and 110 grams per liter ofphenol. It is to be understood that the pyridine sulphate solution alsocontains, in sulphate form, any tar bases that were in the washedfraction, and that the phenol includes the neutral oils and gummycompounds previously discussed. This solution is then. cooled to from to35 C.

Fifteen gallons of the acid washed oil fraction are then cooled to from20 to 35 0., and are added to the cooled pyridine sulphate solution, andthe mixture thoroughly agitated for 15 minutes. Agitation is thenstopped and the mixture settles into two layers, the bottom layer beinga clear, amber pyridine sulphate solution, with a volume of from togallons and containing 42 grams per liter of phenol, and the top layerbeing a dark red oil.

This pyridine sulphate solution thus obtained is suitable forrectification with steam for the purpose of reducing the phenol to thelow concentration necessary to permit recovery of pyridine from thesulphate solution by springing it with an alkali.

We claim:

1. A method of recovering pyridine bases from a coal tar distillationoil fraction containing said bases along with at least 2% phenol andsmall Volumes of other constituents that are soluble in said phenol;said method comprising washing said fraction with dilute sulphuric acidat a temperature of from 60 to 100 C. until a solution is obtainedcontaining in equilibrium concentration pyridine sulphate and saidphenol with said constituents dissolved therein, cooling said solutionto a temperature of not more than 40 C., washing said cooled solution ata temperature of not more than 40 C. with a relatively small volume ofsaid fraction to unbalance the equilibrium concentration between saidpyridine sulphate and said phenol and cause material volumes of thelatter to dissolve in said washing fraction along with said constituentsdissolved in said phenol, separating said solution from said smallvolume of said fraction and rectifying said solution with steam toproduce relatively pure pyridine sulphate from which the pyridine basesmay be recovered.

2. A method of recovering coal tar bases from a solution containing thesame and sufficient phenol to combine with said bases and formcomplexes, said method comprising washing said solution With dilutesulphuric acid at temperatures sufiiciently high to decompose saidcomplexes and produce a sulphate solution of said bases containingphenol, cooling said sulphate solution and Washing it with a coal tardistillation oil fraction to absorb said phenol, and separating saidsulphate solution from said fraction as a solution suitable for easypurification by steam rectification.

JOSEPH H. WELLS.

PHILIP J WILSON, JR.

